1. Field of the Invention
The present invention relates to ion exchange resins, more particularly cation exchange resins, and to the process for preparing these resins.
2. Discussion of Background
Ion exchange resins are organic compounds: they are rigid, 3-dimensional polymers in which the polymeric chains are held together by cross-linking groups. This type of resin contains positively and/or negatively charged moieties fixed to the polymer. Associated with each of these fixed charges is an ion of opposite charge that is free to exchange with ions of similar charge in a surrounding solution.
Radioactive cesium-137 is a long-lived fission product found in wastes produced by reprocessing fuels from nuclear reactors. The bulk of this isotope is found in the high-activity waste, but smaller amounts are also found in other waste streams such as the overheads from waste evaporators and the water from fuel cooling basins.
When acidic, high-activity wastes from reprocessing plants are neutralized, as they are in some defense reprocessing plants, insoluble sludges precipitate that contain most of the fission products. There remains, however, a very large volume of soluble material, called the supernate, which is composed principally of sodium nitrate and sodium hydroxide and which contains virtually all of the cesium.
One approach to the ultimate management of such high-activity waste is to remove the cesium from the supernate, combine it with the sludge, and convert them both to glass by vitrification in a joule heated melter. Several cesium-specific phenolic resins, including "DUOLITE CS-100", a trademark of Rohm and Haas, Inc., and another disclosed in U.S. Pat. No. 4,423,159, have been proposed for removal of cesium from supernate. The amounts of these materials required to decontaminate the supernate adequately are too large to be fed directly to the melter. Excessive amounts of organic matter will reduce some of the constituents of the sludge to the metallic state, which in turn will cause an electrical short circuit in the melter. There is thus a need for a more efficient cesium-specific ion exchange resin that will decontaminate the supernate adequately but will not introduce excessive amounts of organic matter into the melter.